1. Field of the Invention
The present invention relates generally to antennas used in wireless local area networks, and more particularly to a dual-band omnidirectional antenna, which has dual-band operating characteristics enabling the antenna to operate in two different frequency bands and omnidirectional radiation characteristics in each of the frequency bands.
2. Description of the Prior Art
Generally, Wireless Local Area Networks (WLANs) are used to transmit and receive digitally formatted data in a wireless manner between areas in a building, between different buildings, or between a building and an external area using wireless communication devices. In WLAN systems, antennas which operate in corresponding frequency bands are required for wireless communication devices.
Meanwhile, WLAN systems are classified into an Institute of Electrical and Electronics Engineers (IEEE) 802.11b system in which a representative operating frequency is 2.4 GHz and an IEEE 802.11a system in which a representative operating frequency is 5.725 GHz, depending on international standards for operating frequencies. Further, each wireless communication device currently used in WLAN systems is generally provided with two antennas. That is, one antenna operating in the 2 GHz frequency band, and the other antenna operating in the 5 GHz frequency band are separately provided. Such a double-antenna structure is designed to enable the wireless communication device to be compatibly used in both the two WLAN systems, but it is very disadvantageous in structural and economic aspects. Accordingly, there is urgently required an antenna capable of being compatibly used in both the two WLAN systems, that is, a so-called dual-band antenna capable of operating in different frequency hands used in the two WLAN systems.
Meanwhile, the WLAN systems enable communications between different devices, such as between personal computers, between a personal computer and a server, between a personal computer and a printer, etc. In this case, individual stations can be randomly located, in relation to other integrated stations. Therefore, the dual-band antenna must have omidirectionality.
In the prior art related to antennas, a ceramic patch antenna designed to have dual-band operating characteristics is disclosed. The patch antenna typically comprises a ceramic substrate, a metalized patch formed on one surface of the ceramic substrate, and a ground plane arranged on an opposite surface thereof. While the ceramic patch antenna can be actually miniaturized, it is very expensive relative to a dipole antenna. Further, the ceramic patch antenna requires special connector and cable, and the requirement for the special connector and cable is accompanied with a burden of additional installation costs. Especially, since the patch antenna has directional radiation characteristics, it is not suitable for wireless LANs requiring omnidirectional radiation characteristics.